Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $126.46   7.533%   $135.9862   $135.99   $136.00   $136.00  
  Purchase #2 $204.38   3.705%   $211.9523   $211.95   $211.95   $212.00  
  Purchase #3 $187.48   6.531%   $199.7243   $199.72   $199.70   $199.70  
  Purchase #4 $213.74   13.188%   $241.928   $241.93   $241.95   $241.90  
  Purchase #5 $15.78   9.152%   $17.2242   $17.22   $17.20   $17.20  
  Purchase #6 $8.60   12.259%   $9.6543   $9.65   $9.65   $9.70  
  Purchase #7 $222.61   13.307%   $252.2327   $252.23   $252.25   $252.20  
  7 purchase totals = $979.05       $1,068.7020   $1,068.69   $1,068.70   $1,068.70